1. Field of the Invention
The invention relates to a process for the preparation of polycarbonate polyols by immortal polymerisation of cyclic carbonates in the presence of double metal cyanide catalysts (DMC catalysts) and chain-transfer agents consisting of polyether carbonate polyols.
2. Description of Related Art
An immortal polymerisation within the scope of the invention means a ring-opening polymerisation, wherein cyclic carbonate reacts in the presence of chain-transfer molecules with ring opening. The polymerisation is referred to as immortal when the polymerisation takes place, in the ideal case, without chain termination reactions and the number of macromolecules generated is equal to the number of chain-transfer molecules used. In an immortal polymerisation, the molecular weight of the macromolecules that are generated can be adjusted via the ratio of the number of monomer molecules used to the number of chain-transfer molecules. The functionality of the macromolecules that are generated is determined by the functionality of the chain-transfer molecules.
Polymer (1992), 33(9), 1941-1948 describes the living polymerisation of neopentyl glycol carbonate with tetraphenylporphyrin-aluminium complexes as catalyst. Because the reaction was carried out without the use of chain-transfer agents, the molecular weight of the macromolecules that are generated is determined by the number of catalyst molecules. A disadvantage is that the functionality of the macromolecules that are generated is not controlled. Other disadvantages are the sensitivity of the catalyst to traces of water, and the poor industrial availability of the catalyst.
Journal of Polymer Science, Part A (2000), 38(16), 2861-2871 describes the immortal polymerisation of epoxides, lactones and methacrylic acid esters with aluminium metalloporphyrins and episulfides with zinc metalloporphyrins. It is characterised by the use of protic compounds such as carboxylic acids and HCl as chain-transfer agent. The use of alcohols as chain-transfer agent is limited to epoxides and lactones, the catalysts that are used being sensitive to large amounts of alcohol groups and low molecular weight alcohols therefore being unsuitable as starter. Other disadvantages are the sensitivity of the catalyst to traces of water, and the poor industrial availability of the catalyst. Experimental details are not mentioned in the publication.
Macromolecules (2001), 34(18), 6196-6201 describes the immortal polymerisation of lactones and lactides with aluminium complexes as catalyst. The use of benzyl alcohol as a monofunctional chain-transfer molecule is a disadvantage. Other disadvantages are the sensitivity of the catalyst to traces of water, and the poor industrial availability of the catalyst.
Chemistry—A European Journal (2008), 14 (29), 8772-8775 describes the immortal polymerisation of trimethylene carbonate using benzyl alcohol as chain-transfer agent. The use of a monofunctional chain-transfer molecule is a disadvantage. Macromol. Rapid Commun (2009), 30, 2128-2135 describes the use of dihydroxy compounds as starter. A disadvantage in both works is the use of zinc-imidate complexes as catalysts, which are not readily available industrially and are sensitive to air, so that strict inertisation is necessary for the reaction.
EP-A 1859863 and DE-A 10108485 describe the conditioning of DMC (double metal cyanide) catalysts for the polymerisation of epoxides. It is a disadvantage that the catalysts in this reaction are sensitive to the large amounts of alcohol groups in the starters, and low molecular weight alcohols are therefore unsuitable as starter.
WO-A 03/014186 discloses the DMC-catalysed ring-opening homo- and co-polymerisation of cyclic carbonates, optionally in the presence of one or more starter compounds (chain-transfer agents), there being disclosed as chain-transfer agents inter alia polyether polyols and polyester polyols. Polyether carbonates as chain-transfer agents are not disclosed, however.